As Chris Cillizza notices, whenever she speaks, the default tenor of her voice is sarcastic:

"Palin
is more comfortable playing to those who already love her rather than
to reaching out to those who take a more skeptical stance. Sarcasm rarely plays well in politics -- particularly among the
independent voters who typically decide elections. It's why naturally
sarcastic pols -- President Obama among them -- largely avoid any
wise-cracking in public."

For me, it's not just the sarcasm of her speaking style that's noticeable; it's the intended targets.
Palin's enemies are almost always Beltway elites -- not really just Democrats, but broadly Those Who Know Better Than You. Palin often seems to
address the editors, producers, and
photographers at the back of the room (at times she's even addressed them directly). Her stump speeches read as one
long litany of "gotchas" at the elite media.

This is understandable, to a point: Palin believes her vice-presidential campaign, like her conservative agenda generally, was screwed over by the Beltway crowd. She also knows that such rhetoric touches her audience's anti-elite trigger points. But Palin's sarcasm often joins up with a less desultory sentiment: personal victimhood.
She was wronged, and her post-election political rebirth on the public speaking circuit, with all the adulation of the crowds that's come with it, seems to be, above all, about getting revenge.

The problem is, her speeches are satisfying in the moment but they have no resonance -- because they're all about her. Palin has the self-confidence of the millennial generation, and the fire of the baby boom generation, but she gives speeches like she's a Gen-X slacker. If
she wants to be president, she has to channel the idealism of the
boomers, and the sarcasm of Gen X, but focus them not on her enemies, or on the
wrongs done to her, but on corruption in government. She's capable of this, but she doesn't seem
to want to go there.

This is one reason why Palin seems to attract the largest crowds but doesn't have the high approval ratings or straw poll wins to match.